The present invention relates generally to amplifiers, and more particularly to power amplifiers employing multiple output devices which are operated from several power sources of differing supply voltages in order to increase the operating efficiency of the amplifier.
There are many applications in which it is desirable or necessary to provide an amplifier which is capable of providing high amplitude output signals. It is also desirable, of course, that such an amplifier operate as efficiently as possible. Unfortunately, these considerations are generally contradictory, since the availability of higher output signal levels generally requires that the output devices operate at higher levels of power dissipation. One manner in which these contradictory considerations have been reconciled in the past is to utilize several output devices which are connected to power sources which provide differing voltage levels. When only low amplitude output signals are called for, the lower power device provides the necessary low level output signals, and the higher power device is cut off. When higher amplitude output signals are called for, however, the low power device will be driven into saturation, and the higher power device will be called into play. This results in quite high efficiency, since the higher power device is only utilized during those transitory periods when high power is called for from the amplifier.